The present invention relates to inflatable protective cushions, and more specifically relates to cushions formed to contract along a major axis upon inflation. This type of cushion is particularly useful in side protection of occupants in a transportation vehicle, such as an automobile. A process for forming the cushion in an optimum shape according to the present invention is also provided.
Inflatable protective cushions used in passenger vehicles are part of a relatively complex passive restraint system. The main elements of this system are: an impact sensing system, an ignition system, a propellant, an attachment device, a system enclosure, and an inflatable protective cushion. When the impact sensing system senses an impact, the propellant is ignited by the ignition system causing an explosive release of gases that inflate the protective cushion, driving it from the system enclosure to a deployed state proximate to the vehicle occupant where it can absorb the impact of the movement of the occupant against it and dissipate its energy by means of rapid venting of the gas. The entire sequence of events from sensing the impact to deflation occurs within about 30 milliseconds.
A typical construction material for airbags has been a polyester or nylon fabric, coated with an elastomer such as neoprene, or silicone. The fabric used in bags is typically a woven fabric formed from synthetic yarn by weaving practices that are well known in the art. The inflation medium is generally a nitrogen or helium gas generated from a gas generator or inflator. Gas is conveyed into the cushion at a relatively warm temperature. The coating obstructs the permeation of the fabric by the gas, thereby permitting the cushion to rapidly inflate without undue decompression during a collision event. In the un-deployed state, the cushion is most commonly stored in or near the steering column, the dashboard, in a door panel, or in the back of a front seat placing the cushion in close proximity to the person or object it is to protect.
The use of a coating material for the airbag fabric has found acceptance because it acts as an impermeable barrier to the inflation medium. Airbags may also be formed from uncoated fabric that has been woven in a manner that creates a product possessing low permeability or from fabric that has undergone treatment such as calendaring to reduce permeability.
Silicone coatings typically utilize either solvent based or complex two component reaction systems. Dry coating weights for silicone have been in the range of about 3 to 4 ounces per square yard or greater for both the front and back panels of side curtain airbags. The majority of commercially used restraint cushions are formed of woven fabric materials utilizing multifilament synthetic yarns of materials such as polyester, nylon 6 or nylon 6,6 polymers.
The driver-side airbags are typically of a relatively simple configuration in that they function over a fairly small well-defined area between the driver and the steering column. One such configuration is disclosed in U.S. Pat. No. 5,533,755 to Nelsen et al., issued Jul. 9, 1996, the teachings of which are incorporated herein by reference. However, inflatable cushions for use in the protection of passengers against frontal or side impacts must generally have a more complex configuration since the position of a passenger may not be well-defined and a greater distance may exist between the passenger and the surface of the vehicle against which that passenger might be thrown in the event of a collision.
As eluded to above, in addition to driver-side and passenger-side airbags, there are side impact airbags and side curtain airbags. Side impact airbags are linear, inflatable tubular structures; side curtain airbags are panel-like inflatable structures that cover a larger area. These both have been designed primarily to protect passengers during side crashes and to provide rollover protection, unrolling from a packed condition in enclosures within the roofline along the side windows of an automobile.
Side impact airbags provide cushioning effects from impact of the head of the passenger when the vehicle in which the passenger is riding is struck from the side. Side curtain airbags not only provide cushioning effects but also provide protection from broken glass and other debris. Both types of airbags provide restraint in addition to cushioning effects during rollover or when the windows of the vehicle are open. As such, it is imperative that side curtain airbags, as noted above, retain large amounts of gas, as well as high gas pressures, to remain inflated throughout the longer time periods of the entire potential rollover situation. To accomplish this, these side curtains are generally coated with very large amounts of sealing materials on both the front and back. Since most side curtain airbag fabrics comprise woven blanks that are either sewn, sealed, or integrally woven together, discrete areas of potentially high leakage of gas are prevalent, particularly at and around the seams.
In addition to the duration of air retention, side impact airbags and side curtain airbags must be able to contract upon inflation to achieve a high degree of tension to restrain vehicle occupants against the lateral forces on the vehicle. Ideally, this tension should be as high as possible, and, moreover, be sufficiently high with relatively low amounts of air in the airbag so that, even while still inflating, they provide restraint against lateral forces.
Several different inflatable tubular structures have been described in the prior art. For example, U.S. Pat. No. 5,480,181, issued to Bark et al., and U.S. Pat. No. 5,322,322, issued to Bark, both describe a braided tube with an inner bladder. U.S. Pat. No. 6,237,942 issued to Swann, describes a tubular structure with longitudinal slits and in inner bladder. Both of these structures achieve a contraction in the longitudinal direction by expanding in the lateral direction upon inflation. U.S. Pat. No. 5,841,564 issued to McDunn et al, describes a tubular structure with constricting elements to restrict the expansion of the tube. Upon inflation, the tubular structure forms a shape that resembles a string of beads as it contracts. Another technique that is used to achieve contraction upon inflation is to use a series of parallel cylindrical chambers. These tubular structures are also used to tension side curtain airbags. However, there still remains a need to increase tension of side impact and side curtain airbags especially at low volumes.